Environ. Sci. Technol. 1993, 27, 128-133
(16) Speer, R. E.; Peterson, K. A.; Ellestad, T. G.; Durham, J. L. J. Geophys. Res. 1985, 90, 2119. (17) BucMey, D. J.; Desjardins, R. L.; Lalonde, J. L. M.; Brunke, R. Comput. Electron. Agric. 1988, 2, 243. (18) Businger, J. A.; Oncley, S. P. J. Atmos. Oceanic Technol. 1990, 7, 349. (19) Thornthwaite, C. W.; Holzman, B. Mon. Weather Rev. 1939, 67, 4. (20) Pruitt, W. 0.;Morgan, D. L.; Lourence, F. J. Q. J . R. Meteorol. SOC.1973, 99, 370. (21) Majewski, M. S.; McChesney, M. M.; Seiber, J. N. Environ. Toxicol. Chem. 1991, 10, 301. (22) MacPherson, J. I.; Desjardins, R. L. Proceeding of the seventh AMS symposium of meteorological observations and instrumentation. New Orleans, LA, Jan 1991; Vol. 6. (23) Chahuneau, F.; Desjardins, R. L.; Brach, E.; Verdon, R. J. Atmos. Oceanic Technol. 1989, 6, 193. (24) Webb, E. K.; Pearman, G. I.; Leuning, R. Q. J. R. Meteorol. SOC.1980, 106, 85. (25) Pattey, E.; Desjardins, R. L.; Boudreau, F.; Rochette, P. Boundary-Layer Meteorol. 1991, 89, 195. (26) Schuepp, P. H.; Leclerc, M. Y.; MacPherson, J. I.; Des-
jardins, R. L. Boundary-Layer Meteorol. 1989, 50, 356. (27) Leclerc, M. Y.; Thurtell, G. W. Boundary-Layer Meteorol. 1990, 52, 247. (28) Turner, B. C.; Glotfelty, D. E. Anal. Chem. 1977, 49, 7. (29) Lourence, F. J.; Pruitt, W. 0. J. Appl. Meteorol. 1969,8, 492. (30) Spencer,W. F.; Cliath, M. M. J. Agric. Food Chem. 1974, 22,987. (31) Bardsley, C . E.; Savage, K. E.; Walker, J. C. Agron. J. 1968, 60, 89. (32) Spencer, W. F.; Farmer, W. J.; Jury, W. A. Environ. Toxicol. Chem. 1982,1, 17. (33) Woodrow, J. E.; Crosby, D. G.; Mast, T.; Moilanen, K. W.; Seiber, J. N. J. Agric. Food Chem. 1978, 26, 1312. (34) Probst, G. W.; Golab, T.; Herberg, R. J.; Holzer, F. J.; Parka, S. J.; Van der Schans, C.; Tepes, J. B. J. Agric. Food Chem. 1967, 15, 592. Received for review March 12,1992. Revised manuscript received August 18,1992. Accepted September 4,1992. Land Resources Research Center Contribution No. 92-84, Agriculture Canada.
Absorption of NO Promoted by Strong Oxidizing Agents: Organic Tertiary Hydroperoxides in n -Hexadecane Howard D. Perlmutter," Huihong Ao, and Henry Shaw
Department of Chemical Engineering, Chemistry & Environmental Science, New Jersey Institute of Technology, University Heights, New Jersey 07102 The selective removal of nitric oxide from gas streams was investigated using 3,6-dimethyl-3-octylhydroperoxide, p-menthanyl hydroperoxide, pinanyl hydroperoxide, and cumenyl hydroperoxide in solutions of n-hexadecane (cetane). The influence of different variables such as temperature, gas stream flow rate (or residence time), and concentration of hydroperoxide compounds on rate of NO removal was evaluated. The NO reacted with the hydroperoxides to produce alkyl nitrates. These are easily hydrolyzed with ammonium hydroxide to ammonium nitrate and the alcohol. The hydroperoxides used in this study were selected to be inexpensive, be commercially available, have a relatively low vapor pressure to avoid loss of reagent when in contact with hot flue gas, and be easily regenerated. Under the same conditions, cumenyl and pinanyl hydroperoxide removed NO faster than the other two organic hydroperoxides tested. The highest rates of NO removal were obtained at the highest temperatures, concentrations, and residence times. Introduction Nitrogen oxides (NO,) are mixtures of compounds of nitrogen and oxygen generally found in effluents from combustion sources. The predominant NO, compounds are NO and NOz. They are formed as a result of the reactions of atmospheric nitrogen with atmospheric oxygen at very high temperatures. Also, large quantities of NO, are formed from the oxidation of nitrogen compounds found in fuel or in wastes being incinerated. More than 90% of NO, emitted from stationary combustion sources consist of NO, which is relatively insoluble in inorganic aqueous solutions. Finding a way to control NO is essential for the prevention of NO, pollution, one of the major sources of acid rain. One of the most difficult problems related to pollution control from boilers and incinerators is reducing the 128
Environ. Sci. Technol., Vol. 27, No. 1, 1993
emissions of the oxides of nitrogen. The NO, emissions that result from the high-temperature oxidation of the nitrogen in the combustion air can be partly controlled by combustion modification techniques and by postcombustion methods. Postcombustion methods include selective catalytic reduction (SCR), thermal NO, removal, and scrubbing. Research on NO,-scrubbing processes has shown that these processes require expensive oxidation reagents and may present special disposal problems because of high concentrations of chlorides, nitrates, and nitrites in the aqueous effluents. However, scrubbing promises to be less expensive than competing posttreatment technologies and has the advantage that the same scrubber could be used to control other acid gases and particulates. No specific techniques have been developed for controlling the extremely high concentration of NO, emissions that results from the oxidation of nitrogen compounds found in industrial and agricultural substances being incinerated. SCR systems have not been demonstrated for high NO, concentrations and are easily poisoned by substances present in hazardous wastes. In the case of industrial incineration, NO, emissions resulting from nitrogen compounds have been found in excess of 8000 ppm (1). In addition to NO,, scrubbers should be designed to control other acidic effluents such as oxides of sulfur (SO,), hydrogen chloride (HCl), phosphorus pentoxide (P?O,), and inorganic particulate matter containing transltion metals (2, 3). A number of aqueous inorganic solutions have shown high capacity for NOz absorption, but NO is absorbed with difficulty. Consequently, a method to oxidize NO to NO2 or an equivalent oxidized state of nitrogen is required to substantially reduce NO, emissions. Aqueous solutions of a number of oxidizing agents have been studied to determine their effectiveness in removing NO, and SO, from
0013-936X/93/0927-0128$04.00/0
0 1992 American Chemical Society
flue gas ( 4 ) , including processes using acidic H202(5), alkaline solutions of NaC102 (6),and peracids (7). We report the development of a totally organic scrubbing system for NO, removal under simulated flue gas conditions. We have found that dilute solutins of nonvolatile tertiary organic hydroperoxides (ROOH) in nhexadecane (cetane) effectively absorb nitric oxide to form alkyl nitrates (RON02)which can be efficiently denitrated by aqueous hydrolysis. Much of the known chemistry of NO, in the presence of ROOH is the result of the study of the photooxidative reactions of ROO' in the atmosphere, illustrated by eqs 1-3 (8-11). In a study of the condensed-phase reactions RO2' + NO --* RO' + NO2 (1) RO2' + NO2 RO2NO2 (2)
-
y
s
CH,-CHa-C-C4 -CH,-YH-CH,-CY I
O-OH
CH,
(1) 3.6-dime th yl-3 -0c 1yl hydroperoxide
(2) p-menthane hydroperoxide ( m i x 0 1 SIoreoiJomsr1a I e r l . h y d r o p e r o x i d e s )
+
RO'
+ NO2
RON02
(3)
of NO with hydroperoxides, Shelton and Kapczewski reported that reaction of 100% NO with tert-butyl hydroperoxide in benzene produced tert-butyl nitrate and tert-butyl nitrite via a four-step NO-induced free-radical reaction sequence, shown in eqs 4-8 (12). This reaction
+ NO
-
Me3CO' + Me3COOH Me3COO'
+ NO
Me3COH
Me3CO' + HONO
+ -+ - - +
Me3COOH
Me3COH
[Me3COONO]
HONO
Me3COO' (5)
Me3CON02
Me,CONO
(4)
H20
(6) (7)
net reaction: 2(CH3)3COOH + 2N0 (CH3)3CON02 + (CH3)3CONO + HzO (8) was not run under typical flue gas conditions, Le., elevated temperature and a more dilute NO, stream. A successful NO,-scrubbing hydroperoxide candidate would have to fulfill the following requirements: 1. The hydroperoxide should be tertiary (R3COOH). Hydroperoxides (ROOH) as a class of organic oxidizing agents are safer (i,e., thermally more stable) than peroxides (ROOR) (13-15),the former having a tl of 10 h -170 "C, whereas the latter have tllz of 10 h at 120 "C or less (14). Tertiary hydroperoxides,i.e., ones lacking any a-hydrogens, are thermally less labile than secondary and primary analogs and are safe enough to fulfill ICC requirements for handling and transport (15). 2. The hydroperoxide should be relatively inexpensive. This is important because an efficient NO, scrubber (190% removal) should cost no more than $1000015000/ton of NO, removal if it is expected to be economically competitive with selective catalytic reduction (16). 3. The components of the scrubber solution should be nonvolatile, Le., should not be vaporized at flue gas temperatures. 4. The "spent" scrubbing solution should be easily denitrated and the denitrated organic material reoxidized to hydroperoxide and/or used in another economically advantageous way. With these factors in mind, we chose the following four hydroperoxides for our study: 3,6-dimethyl-3-octyl hydroperoxide (l),p-menthanyl hydroperoxide (2), pinanyl hydroperoxide (3), and cumenyl hydroperoxide (4). Experimental Section Starting Materials. (a) 3,6-Dimethyl-3-octyl Hydroperoxide (1) (27,28). To a vigorously stirred mixture of 870 g of 85% H3P04and 516 g of 50% HzOzwas added,
VooH ( 4 ) Curnene hydroperoxide
( 3 ) Pinane hydroperoxide (mix o/ epimers\
over 30 min, 300 g of 3,6-dimethyl-3-octanol. The reaction mixture was stirred at 44 "C for 3 days. The upper organic layer was dissolved in 525 mL of ethyl ether. The ether solution was washed in sequence with distilled water, 5% NaHC03, and distilled water and was then dried over anhydrous MgSO,. The dried ether solution was concentrated in vacuo to yield 291 g of colorless liquid. Iodometric analysis (19) showed 95% hydroperoxide. This material was used without further purification. (b) Commercial Hydroperoxides. p-Menthanyl hydroperoxide (2), pinanyl hydroperoxide (3), and cumenyl hydroperoxide (4) were obtained from Atochem North America, SCN/Glidco, and Aldrich Chemical Co., respectively, and were used without further purification. Physical, chemical, and analytical data for the hydroperoxides are shown in Table I. (c) Gases. The nitric oxide, helium, and NO/He gas mixtures were purchased from Liquid Carbonic Co. and used directly from the cylinder. (d) Other Chemicals. The cetane (n-hexadecane)used as a solvent for the hydroperoxides was purchased from Aldrich Chemical Co. and used without further purification. The tert-butyl nitrite and isobutyl nitrate used as standards for the qualitative and quantitative determination (N material balance) of the scrubbing products were obtained from Aldrich Chemical Co. and used without further purification. Scrubbing Experiment Apparatus. The experiments were conducted in a laboratory-scale scrubber reactor system shown in Figure 1. The basic scrubbing apparatus consists of a 2.54 cm diameter by 56 cm long glass pipe as the scrubber reactor. The flow rates of inlet gases were measured with two calibrated Cole Parmer rotameters. Heating tape connected to a temperature controller was used to warm the reactor. The reactor temperature was monitored by a Chromel-Alumel thermocouple inserted between reactor and heating tape. To avoid the organic moisture condensing in the analytical system, an ice bath containing a glass U-tube was used. Procedure for Feed and Effluent Nitric Oxide Analysis. A measured quantity of organic hydroperoxide Environ. Sci. Technol., Vol. 27, No. 1, 1993
129
Table I. Analytical, Physical, and Stability Data for the Hydroperoxides
cost/lb,"
compound
$
3,6-dimethyl-3-octyl hydroperoxide (I) p-menthanyl hydroperoxide (2)
tilz at % 120°C>ch OOHb
bp,"
% composition"
O C
>200
95 >50
2
56
pinanyl hydroperoxide (3)
1.50
100
42
cumenyl hydroperoxide (4)
0.80
>500
70
55 5-30 15-20 41 55 4 70
26 3 1
mixture of 6 stereoisomeric tertiary hydroperoxides p-methane (diluent) various cyclohexanones, acetone, alcohols, hydrocarbons 2 epimeric hydroperoxides 2 epimeric pinanes (diluent) pinanols cumene hydroperoxide cumene (diluent) a,a-dimethylbenzyl alcohol acetophenone, water
-
>200 180
180 160 >200 155
"Obtained from manufacturer. * Iodometric analysis (19). 'Reference 15; t l j z(half-life) = In a/first-order rate constant for disappearance of the hydroperoxide.
1 ?i1 A $6
FLOW METER
HOOD
..:
NO IN He
TCD/GC
*.
Table 11. NO-Removing Ability of Hydroperoxides"
concn, M
conversn,
oxidizer 3,6-dimethyl-3-octyl hydroperoxide (1) menthanyl hydroperoxide (2) pinanyl hydroperoxide (3) cumenyl hydroperoxide (4)
0.300 0.296 0.306 0.303
44.6 49.7 79.4 84.2
%
" N O inlet concentration, 1500 ppm in He; gas flow rate, 1000 cm3/min; operating temperature, 90 "C; solution volume, 200 mL.
He
SCRUBBER
FRITTED DISK
Figure 1. Flow schematic of NO, scrubbing unit.
solution was poured into the reactor. Then pure helium gas was bubbled through the solution to purge the flow system of air trapped during the filling process. While He was bubbling, the solution was heated to the desired operating temperature. A known concentration of nitric oxide gas replaced the bubbling helium as the timer was started for the experiment. Part of the effluent gas was passed through an ice bath to condense the organic vapor and then analyzed either by an on-line gas chromatograph with a thermal conductivity detector or by a chemiluminescent NO, analyzer. The feed concentration was checked periodically during the experiment by bypassing the reactor and sending part of the feed gas directly to the analytical train. Product Analysis of Scrubbing Solution and Gaseous Effluent. (a) Volatile Nitrogen (Le., NOz) and 02.Three methods were used to detect NOz in the exit gases from the scrubbing experiment: gas chromatography, NO, chemiluminescence analysis, and aqueous alkaline scrubbing of exit gas followed by ion chromatographic (IC) analysis for NO3-. Gas chromatography was used to detect any O2resulting from hydroperoxide thermal decomposition. (b) Nonvolatile Nitrogen [i.e., Alkyl Nitrites (RONO) and Alkyl Nitrates (RONOZ)]. Qualitative and quantitative determination of organic nitrate and nitrite esters was achieved using Fourier transform infrared spectroscopy (FTIR). Both nitrates and nitrites show strong absorption bands at 1630-1640 cm-l. However, nitrate also absorbs at 1300 and 860 cm-l, whereas nitrites evince only a peak at 760 cm-l(12,20,21). Concentrations of these materials in the scrubbing solutions was determined by comparing band intensities with standard tertbutyl nitrite and isobutyl nitrate solutions of known concentration in cetane. 130
Envlron. Scl. Technoi., Vol. 27, No. 1, 1993
100
Conversion %
90
80 70 60 50
40 30 20
10
X
3,6dirnethy13octyl(l)
A
Curnene(4)
0 20
30
40
50 60 Temperature,
80
90
100
C
Figure 2. Effect of temperature on removing NO with 200 cm3 of solutions contalnlng 0.3 M plnanyl hydroperoxlde (3), 0.3 M 3,6dlmethyl-3octyl hydroperoxide (I), or 0.3 M cumenyl hydroperoxide In n-hexadecane. The feed gas contained 1500 ppm(v) NO In N2and was metered at 150 cm3/min.
Denitration Procedure. A 2-mL aliquot of a scrubbing solution of 0.494 M menthanyl hydroperoxide (2) in cetane which had taken up NO was mixed with 20 mL of 10% aqueous ammonia. The resulting heterogeneous mixture was vigorously stirred at 70 "Cfor 24 h. The mixture wa8 allowed to cool to room temperature. The upper organic layer was dried over anhydrous granular Na2S0, and taken for FTIR analysis. The lower layer was taken for IC analysis. Results and Discussion The relative NO-removing capabilities of hydroperoxides 1-4, shown in Table 11, clearly demonstrate that pinanyl (3) and cumenyl hydroperoxides (4) are superior to 1 and 2. The synthetic material 1 clearly suffers from the fact that it is expensive to make, as well as thermally unstable at temperatures
